The present invention relates to a communication apparatus used in a digital mobile communication system, specifically, relates to a communication apparatus which uses a known signal (midamble) to carry out channel estimation.
In a digital mobile communication system based on 3GPP/TDD technology, a known signal called (Midamble) which is used for carrying out channel estimation has been proposed. In a mobile communication system which adopts a midamble, since each user utilizes an individual midamble based on a code which is generated by sequentially time-shifting a basic code, there is a feature that it is possible, in a base station apparatus, to calculate the correlation of each user""s individual midamble using only one correlator of the basic code. Therefore, it is possible to execute channel estimation of each user in base station apparatus.
However, since the length of the midamble assigned to each user increases as the number of users increases, the ratio of the information signal within slot decreases. Consequently, there is a problem of degrading the communication efficiency of the system.
Aiming at solving such a problem, a known signal which is employed commonly among users, namely, common midamble and which is used for channel estimation is introduced. In the mobile communication system using such a common midamble, abase station apparatus transmits a signal which includes a data part and midamble part (common midamble among users) to each user, and each user (each communication terminal apparatus) carries out channel estimation using the common midamble included in the signal transmitted by base station apparatus.
However, a mobile communication system using the aforementioned conventional common midamble has the following problem. That is, according to the current 3GPP/TDD specifications, it is specified that transmitting power of the data portion and midamble portion are equal within a slot when adopting the common midamble. Since the transmitting power of the data portion in the signal transmitted to each user cannot be individually controlled as, according to the specification, the transmitting power of the midamble portion and data portion are equal, hence, it is impossible to perform transmitting power control.
Consequently, because the receiving power of the data portion and midamble portion decreases which leads to user of bad communication quality (for instance, user which exists at a position far from base station apparatus), both channel estimation accuracy and data portion receiving quality are deteriorated. To improve the receiving quality of the user of bad communication quality, a method to increase the transmitting power of the data portion and midamble portion can be adopted. However, even if the receiving quality of a user in a cell serviced by a base station apparatus can be improved when adopting such a method, interference to cells serviced by other base station apparatuses thereby will be enlarged.
While cancelling the interference to other cells in a mobile communication system using a conventional common midamble, as mentioned above, there is a problem that it is difficult to appropriately control the transmitting power of midamble portion and data portion in the signal transmitted to each user so that receiving quality of each user may be improved.
It is an object of the present invention to provide a base station apparatus which appropriately controls the transmission power of a data portion and midamble portion in a signal transmitted to each communication terminal apparatus in order to improve the reception quality of each communication terminal apparatus while cancelling the interference to other cells.
This object can be achieved either to consider a data portion of a signal transmitted to a predetermined communication terminal apparatus while controlling the transmission power according to closed-loop transmission power control based on the reception quality of the aforementioned communication terminal apparatus or to consider a midamble portion of a signal transmitted to a predetermined communication terminal apparatus while controlling the transmission power to be common among all communication terminal apparatuses based on transmitting power value of the data portion of the signal transmitted to all communication terminal apparatuses.